In compressed air braking systems, such as those used on commercial vehicles, an air dryer is typically placed in line after the compressor and prior to the rest of the components, such as the compressed air reservoir or air brake units. The air dryer removes harmful contaminants, such as dirt, oil, oil vapor, water and water vapor, from the compressed air, and thus provides clean, dry air to the components of the brake system. Clean dry air increases the reliability and life of the brake system, thereby reducing maintenance costs.
A typical air dryer used in air braking systems contains a desiccant canister, which includes an oil separator and a desiccant material that adsorbs water as the compressed air passes through it. The desiccant material can be regenerated by reversing the air flow and purging the material with dry air supplied from a purge air volume. As the dry air passes through the desiccant material the moisture that was previously adsorbed from the compressed air is transferred back to the air and expelled through an exhaust port.
The purge volume may be either coupled with the brake system reservoir or contained in a separate purge air reservoir. Air dryers with a separate purge air reservoir may be either integrated or remote. An integrated air dryer system, such as the Bendix AD-IS air dryer, has an air dryer with a self contained purge reservoir tank. A remote purge volume air dryer has the purge air reservoir located remotely from the air dryer.
Remote purge volume air dryers are typically preferred over integrated air dryers, since integrated air dryers tend to be larger and more expensive to make. In addition, the size of an integrated air dryer limits the available mounting areas on the vehicle. In addition to the size of the air dryer, other factors contribute to the limited available mounting area. For example, the air dryer must be located far enough away from the compressor so that the temperature at which the air dryer will effectively remove moisture is not exceeded. Furthermore, the air line from the air compressor to the air dryer must slope downward and have as few bends as possible to prevent water from being trapped in the air line and freezing. Thus, it is desirable to have an air dryer that does not use brake system air for its purge cycle and can be easily mounted in a variety of locations.
In addition to the limited mounting location available, current air dryers also have predefined mounting orientations. This is because the air dryers either have mounting holes built into the dryer body, or are provided with standard mounting brackets. As a result, the air dryer can only be mounted in one position. Thus, some air dryers require multiple mounting brackets to be made and stored to facilitate the various mounting positions required by the different types of vehicles.
Furthermore, air dryer canisters have a limited useful life and can only be regenerated a certain number of times before requiring replacement. To facilitate the periodic replacement of the air dryer canister, a convenient mounting location is desirable.